Measuring device



i Fatent r/masunmo nnvicn Charles l-leiman liapian, Montrouge, and Jean Joseph Marc Pelen, Paris, France, assi nors to Qompagnie pour la Fabrication des eoinpteurs et Materiel dUsines a Gaz, Seine, France, a joint-stock company of France Filed Get. 13, 1955, Ser. No. 540,299

Claims priority, application France Oct. 22, 1954 3 Claims. (U. 32443) The present invention relates to devices used for neutralizing or evaluating a magnetic circuit (magnetometers). More specifically, it relates to those devices in which the magnetic field to be controlled produces an unbalancing potential or current in a circuit comprising means responsive to the magnetic field and in which means are provided for generating, by means of this unbalancing potential or current, a direct or rectified current which is self-controlled, so as to produce in a compensating solenoid a magnetic field equal and in opposition to that which it is desired to control, whereby the current is restored to its original balanced condition.

A magnetometer of this type is described in United States patent application No. 370,968 in the name of Charles Heirnan Kaplan.

A general object of the invention is to amplify the direct or rectified current which produces the compensation of the magnetic field to be controlled, by simple and economical means having a high-speed response.

This amplification of the compensating current is necessary in particular when the device of the type in question is used not only for evaluating a magnetic field but also for neutralizing it through bodies of large dimensions, since the neutralizing coil which surrounds said bodies cannot comprise a large number of windings, in order to facilitate its carrying out into practice and for reasons of economy.

More specifically, an ob'ect of the invention is to malce use, as an amplifier, of a direct current generator,

with separate excitation, driven at a constant speed, the armature of which is connected to the terminals of a circuit comprising the compensating solenoid of the magnetometer, whereas the field winding of the said generator is connected to the circuit containing the device which automatically controls the direct or rectified current produced as a result of the un alance caused by the field to be controlled in the circuit comprising element which are responsive to the magnetic field.

Other features and advantages of the invention shall appear from the detailed description which follows, made in reference to the accompanying drawings in which:

Figure 1 is a wiring diagram of a magnetometer making use of the amplifier according to the invention;

Figure 2 is a modification of Figure l, embodying a magnetic amplifier.

Referring to Figure l, the magnetometer comprises in known manner, a generator 31 of alternating current which supplies the primary winding of a transformer 32. The numerals 33a and 3% represent two identical solenoids within the interior of which are respectively located the cores 34a and 34-17 which are made of a ferro-magnetic alloy of high initial permeability. One end of each of these solenoids is connected to one extreme terminal of the secondary of the transformer 32, respectively through the medium of two non-linear resistances 35a, 3512 Whilst the two other extremities are joined together at the point 36. Between this common point 36 and the centre tapping 37 of the secondary winding of the transformer 32, there is inserted a resistance 38 across the terminals of which there is connected the moving coil 3 of a galvanometer, without torsional couple, the spindle 4 of which is coupled to the movable armature 5 of a condenser 10. This condenser comprises two fixed armatures, one of which, 6, is connected to an oscillator 8 which produces between said armature and the earth 9 a high-frequency voltage,and the other of which, 7, is connected to one end of an impedance 11 the other end of which is connected to earth. There is thus obtained at the terminals of the impedance 11 a voltage difference which is a function of the position of the movable armature 5, viz: of the position of the movable coil 3. The voltage across the impedance 11 is applied to the input terminals of an amplifier-detector 12 of any known type which produces a direct current the intensity of which is a function of the voltage across the impedance 11.

Around the two solenoids 33a and 33b there is wound a third compensating solenoid 39. 413 is a winding which compensates the component of a magnetic field perpendicular to its plane. 41 is an ammeter.

According to the invention, the field coil 17 of a generator 15 is connected to the output terminals of the amplifier-detector 12 whereas its armature 16, which is driven at constant speed by the synchronous motor 18 connected to the terminals 19-2ii of a source of alternating current at constant frequency, is connected to the terminals of a circuit comprising the solenoid 39, the winding 40 and the ammeter 41. The magnetization curves of each of these cores being displaced by and being of equal amplitudes, no current passes through the branch 3637. However, if an external magnetic field acts on these cores, the component of this field along their magnetic axis produces a dissymmetry in their magnetization. This dissymmetry causes a distortion of the current curves in the solenoids 33a and 33b. In view of the non-linear resistances 35a and 35b, this causes a rectified current to flow through the resistance 38.

The moving coil 3 deviates, thus causing the capacity of the condenser 14) to vary as a result of the deviation of the movable armature 5. This causes a current variation in the impedance 11 and, consequently, a variation in the voltage at the output terminals of the amplifierdetector 12. The amplifier-detector 12 produces a variable direct current in the field coil 17 of the generator 15. The armature 16 thereof then supplies into circuit 39-40-41 a direct current having such a direction and magnitude that the flux produced by the solenoid 39 exactly compensates the component of the magnetic field acting on the cores 34a and 34-13). This current, measured by the ammeter 41, is proportional to this component. It produces in the coil 49 a magnetic field which neutralizes the outer magnetic field passing therethrough.

The difference of potential at the terminals of the armature 16 depends solely on the current which passes through the moving coil 17 and in the circuit 39-4tl41 there is obtained a current whose intensity is higher than that of the current issuing from the amplifier-detector 12, or better stated, a higher power.

Figure 2 is a modification of Figure 1, said modification consisting in that there is interposed a magnetic amplifier or transducer between the output terminals of the amplifier-detector l2 and the field coil 17 of the generator 15. In said figure (wherein the same numerals have the same significance as those of Figure 1), 2]. designates a magnetic amplifier whose control winding 22 is connected to the terminals of the amplifier-detector 12. The second winding 23 of the magnetic amplifier is connected to the terminals 2526 of a source of alternating current. The field coil 17 of the generator 15 is connected :to a rectifier 24 inserted in the circuit of the V winding 23.

We claim:

1. Magnetometer comprising a first circuit constituted by two identical solenoids each comprising a core having a high initial permeability, by two non-linear resistances respectively in series with each of the said solenoids and by a source of alternating current whose current produces in the said solenoids a magnetic field which saturates the said cores, a compensating solenoid through which passes a current producing in said solenoid a field whose intensity neutralizes the action on the said high initial permeability core of the magnetic field to be measured, a second circuit controlling the current in the said solenoid in function of the unbalancing current passing through the first circuit, the said magnetometer comprising a separate excitation generator driven at constant speed, the armature of which is connected in the circuit terminals of the said impedance, the said magnetometer comprising a separate excitation generator driven at constant speed the armature of which is connected in the circuit comprising the compensating solenoid and the field coil of which is connected to the output terminals of the amplifier-detector.

3. Magnetometer comprising a first circuit constituted by two identical solenoids each comprising a core having a high initial permeability, by two non-linear resistances respectively in series with each of said solenoids, by an alternating current generator, and by a transformer, the two ends of the secondary of which are respectively connected to one end or" the said two solenoids and the mid point of the said secondary of which is connected to the two other ends of the said two solenoids, a compensating solenoid surrounding at least one of the said two solenoids, a galvanometer whose moving coil, without opposing couple, is inserted in the lead connecting the mid-point of the secondary of the transformer to ie common junction point of the two solenoids, an oscillator producing a high frequency voltage, a variable condenser Whose movable armature is integral with the V moving coil of the galvanometer, and which comprises connected to one end of the said two solenoids and the midpoint of the said secondary of which is connected to the two other ends of the said two solenoids, a com oscillator producing a high frequency voltage, a variable element whose movable part is integral with the moving coil of the galvanometer, an impedance, an amplifierdetector whose inlet terminals are connected to the References Cited in the file of this patent UNITED STATES PATENTS 2,446,390 Rath Aug. 3, 1948 2,727,206 Ryerson Dec. 13, 1955 2,832,041 Trachtenberg Apr. 22, 1958 2,836,791 Kaplan May 27 1958 

